Organic light-emitting elements (organic electroluminescent elements or organic EL elements) are each an electronic element including an anode, a cathode, and an organic compound layer placed between both of these electrodes. A hole and electron injected from both the electrodes recombine in the organic compound layer to produce an exciton, and the organic light-emitting element emits light upon return of the exciton to its ground state. Recent advance of the organic light-emitting elements is significant and the advanced light-emitting elements have, for example, the following features. The elements can be driven at low voltages, emit light beams having various wavelengths, have high-speed responsiveness, and can be reduced in thickness and weight.
Of the organic light-emitting elements, a phosphorescent light-emitting element is an organic light-emitting element that: includes, in its organic compound layer, a material that emits phosphorescence; and provides light emission derived from a triplet exciton of the material that emits phosphorescence. In recent years, creation of a novel phosphorescent light-emitting material has been vigorously performed for providing a high-performance phosphorescent light-emitting element.
For example, a trivalent iridium complex having a metal-carbon bond has been frequently used as a guest material for a phosphorescent light-emitting element because of its high phosphorescence quantum yield. Meanwhile, PTL 1 describes an iridium complex shown below in which three different kinds of bidentate ligands coordinate to iridium.
